This invention relates to highly dielectric addition type curable compositions which are less hygroscopic and able to form films and cure into products having improved dielectric properties including a large dielectric constant and a low dielectric loss and finding practical use in a variety of applications.
Engineers have made efforts to ameliorate the performance of electric and electronic parts such as electroluminescent devices and film capacitors while reducing the size and weight thereof. As the dielectric material used therein, organic polymers having a large dielectric constant are of interest and have been used. It is believed that this trend becomes increasingly prevalent in the future.
The dielectric organic polymers which are known in the art include cyanoethyl polysaccharides such as cyanoethyl cellulose, cyanoethyl starch and cyanoethyl pullulan, cyanoethyl polysaccharide derivatives such as cyanoethyl hydroxyethyl cellulose and cyanoethyl glycerol pullulan, cyanoethyl polyols such as cyanoethyl polyvinyl alcohol, and fluoro-resins such as polyvinylidene fluoride.
However, these substances have many drawbacks and do not perform satisfactorily when applied in electric and electronic fields. More particularly, cyanoethyl products of polysaccharides and polysaccharide derivatives and cyanoethyl polyvinyl alcohol have the common drawback that they are highly hygroscopic and readily alter electrical properties by moisture absorption, sometimes detracting from the reliability of electric and electronic parts. This phenomenon can be prohibited by taking such measures as careful control of humidity during the manufacturing process and removal of absorbed water. These measures, however, are regarded negative from the productivity standpoint and hardly expected to exert satisfactory effects.
Also undesirably, cyanoethyl cellulose and cyanoethyl starch are difficult to form film. Cyanoethyl hydroxyethyl cellulose, cyanoethyl glycerol pullulan, and cyanoethyl polyvinyl alcohol undergo large changes of dielectric constant with temperature.
The fluoro-resins such as polyvinylidene fluoride have the advantages of a low moisture absorption and reduced changes of dielectric constant with temperature, but their dielectric constant is approximately half of that of cyanoethyl polysaccharides and polysaccharide derivatives.
U.S. Pat. No. 4,843,517 discloses a highly dielectric organic material base on a cyanoalkyl group-bearing organopoly-siloxane. This is semi-solid or solid and difficult to handle in forming a film. Such difficulty can be avoided by dissolving the material in polar solvents such as acetone and dimethylformamide. However, the solutions are not applicable to various organic resin substrates because the substrates can be attacked by the solvents. The applicable substrates are thus restricted.
An object of the invention is to provide a highly dielectric addition type curable composition which can be prepared as a relatively low viscosity liquid without a need for solvents, which is easy to handle, less hygroscopic, and able to form a film, and which cures into a product having improved dielectric properties including a large dielectric constant and a low dielectric loss.
We have found that an addition type curable composition comprising (A) an organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond, (B) an organohydrogenpolysiloxane containing a cyanoalkyl group, and (C) a platinum group metal catalyst is liquid without a need for solvents, that is, can be prepared to a relatively low viscosity and is thus improved in handling. The composition is less hygroscopic and able to form a film, and cures into a product having improved dielectric properties including a large dielectric constant and a low dielectric loss.
The present invention provides a highly dielectric addition type curable composition comprising (A) an organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond, (B) an organohydrogenpolysiloxane containing a cyanoalkyl group, and (C) a platinum group metal catalyst.
A preferred embodiment of the invention is a highly dielectric addition type curable composition comprising
(A) an organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond, represented by the average compositional formula (I):
R1aR2bR3cSiO(4+a+b+c)/2xe2x80x83xe2x80x83(I)
wherein R1 is a cyanoalkyl group having 3 to 5 carbon atoms, R2 is a monovalent hydrocarbon group of 2 to 6 carbon atoms having an aliphatic unsaturated bond, R3 is a monovalent hydrocarbon group having 1 to 10 carbon atoms other than R1 and R2, letter xe2x80x9caxe2x80x9d is a number of 0.2 to 0.95, xe2x80x9cbxe2x80x9d is a number of 0.05 to 0.7, xe2x80x9ccxe2x80x9d is a number of 0.05 to 1.0, and a+b+c is 1.05 to 1.9,
(B) an organohydrogenpolysiloxane containing a cyanoalkyl group, represented by the average compositional formula (II):
R4kR5mR6nSiO(4+k+m+n)/2xe2x80x83xe2x80x83(II)
wherein R4 is a cyanoalkyl group having 3 to 5 carbon atoms, R5 is hydrogen, R6 is a monovalent hydrocarbon group having 1 to 10 carbon atoms other than R4, letter xe2x80x9ckxe2x80x9d is a number of 0.2 to 0.7, xe2x80x9cmxe2x80x9d is a number of 0.2 to 0.7, xe2x80x9cnxe2x80x9d is a number of 1.0 to 1.6, and k+m+n is 2.0 to 2.3, and
(C) a platinum group metal catalyst.
For the highly dielectric addition type curable compositions of the invention, the presence of nitrile groups is essential. The organopolysiloxane (A) and the organohydrogenpolysiloxane (B) used herein must contain cyanoalkyl groups in their structural units. This is because highly polar nitrile groups are oriented and polarized in an electric field whereby dielectric constant is increased.
Component (A) is an organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond, which is preferably represented by the average compositional formula (I) below.
R1nR2bR3cSiO(4+a+b+c)/2xe2x80x83xe2x80x83(I)
Herein R1 is a cyanoalkyl group having 3 to 5 carbon atoms, R2 is a monovalent hydrocarbon group of 2 to 6 carbon atoms having an aliphatic unsaturated bond, R3 is a monovalent hydrocarbon group having 1 to 10 carbon atoms other than R1 and R2, letter xe2x80x9caxe2x80x9d is a number of 0.2 to 0.95, xe2x80x9cbxe2x80x9d is a number of 0.05 to 0.7, xe2x80x9ccxe2x80x9d is a number of 0.05 to 1.0, and a+b+c is 1.05 to 1.9.
Examples of the C3-C5 cyanoalkyl group represented by R1 include cyanoethyl, cyanopropyl, cyanobutyl, 2-cyanopropyl, 2-cyanobutyl, 3-cyanobutyl, and 2-methyl-2-cyanopropyl. Of these, cyanoethyl is preferred.
Examples of the monovalent C2-C6 hydrocarbon group having an aliphatic unsaturated bond represented by R2 include alkenyl groups such as vinyl and allyl, with vinyl being preferred.
R3 is selected from substituted or unsubstituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, other than R1 and R2, for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl and cyclohexyl, aryl groups such as phenyl, aralkyl groups such as benzyl and phenylethyl, and halogenated monovalent hydrocarbon groups such as chloromethyl, bromoethyl, 3,3,3-trifluoropropyl, 1,1,1-trifluorohexyl and 3-chloropropyl. Of these, methyl is preferred.
The letter xe2x80x9caxe2x80x9d representative of the content of cyanoalkyl groups in the average compositional formula (I) is from 0.2 to 0.95, and preferably from 0.3 to 0.6. Too low a cyanoalkyl content leads to a lower concentration of nitrile groups in the polymer, which may lead to a reduced dielectric constant. With too high a cyanoalkyl content, the content of aliphatic unsaturation-bearing monovalent hydrocarbon groups (represented by xe2x80x9cbxe2x80x9d) may be relatively reduced, resulting in insufficient cure.
The letter xe2x80x9cbxe2x80x9d representative of the content of aliphatic unsaturation-bearing monovalent hydrocarbon groups is from 0.05 to 0.7, and preferably from 0.3 to 0.6. Too low a content of aliphatic unsaturation-bearing monovalent hydrocarbon groups may lead to insufficient cure. With too high a content, the content of cyanoalkyl groups (represented by xe2x80x9caxe2x80x9d) may be relatively reduced, resulting in a lower concentration of nitrile groups in the polymer, which may lead to a reduced dielectric constant.
The letter xe2x80x9ccxe2x80x9d representative of the content of substituted or unsubstituted monovalent hydrocarbon groups other than R1 and R2 is from 0.05 to 1.0, and preferably from 0.6 to 0.9 because too high a content thereof may reduce the content of cyanoalkyl groups or aliphatic unsaturation-bearing monovalent hydrocarbon groups.
The sum of a+b+c, that is the total of cyanoalkyl groups, aliphatic unsaturation-bearing monovalent hydrocarbon groups, and substituted or unsubstituted monovalent hydrocarbon groups other than R1 and R2 in the average compositional formula (I), is from 1.05 to 1.9, and preferably from 1.5 to 1.8. If a+b+c is below the range, the organopolysiloxane may become a very brittle resin. If a+b+c is above the range, the composition may under-cure, precluding film formation.
In preparing the organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond, represented by the average compositional formula (I), any conventional polysiloxane synthesis methods may be used, with no need to limit to a special method. Illustratively, the end product can be obtained by hydrolyzing a silane containing a cyanoalkyl group and a silane containing an aliphatic unsaturation-bearing monovalent hydrocarbon group to form siloxanes, followed by polymerization of the siloxanes or condensation reaction such as alcohol-removal or dehydration reaction.
The silanes, which are used as raw materials for the organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond, should preferably further have at least one hydrolyzable functional group directly attached to a silicon atom. Such hydrolyzable functional groups include halogens, OR, OCOR and NRRxe2x80x2 wherein R and Rxe2x80x2 are hydrogen or alkyl. The alkyl groups represented by R and Rxe2x80x2 are preferably those of 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl and cyclohexyl.
Illustrative examples of the silane having a cyanoalkyl group include monofunctional silanes such as cyanoethyldimethylchlorosilane, cyanopropyldiethylmethoxysilane, cyanoethyldimethylacetoxysilane and dicyanoethylmethylmethoxysilane; difunctional silanes such as cyanoethylchloromethyldichlorosilane, cyanoethylmethyldimethoxysilane, cyanoethyltrifluoropropyldiethoxysilane and cyanopropylphenyldiaminosilane; and trifunctional silanes such as cyanoethyltriethoxysilane and cyanobutyltrimethoxysilane.
Illustrative examples of the silane containing an aliphatic unsaturation-bearing monovalent hydrocarbon group include vinyldimethylmethoxysilane, vinyldimethylethoxysilane, vinylmethyldichlorosilane, vinylmethyldimethoxysilane, vinyltrichlorosilane and vinyltrimethoxysilane.
Other silanes which do not contain a cyanoalkyl group and an aliphatic unsaturation-bearing monovalent hydrocarbon group may also be used as raw materials for the organopolysiloxane. Examples of the other silanes include monofunctional silanes such as trimethylchlorosilane, trimethylmethoxysilane, triethylaminosilane and hexamethyldisilazane; difunctional silanes such as dimethyldichlorosilane, methylphenyldichlorosilane, diphenyldichlorosilane, trifluoropropyldichlorosilane, dimethyldimethoxysilane and chloromethyldiethoxysilane; trifunctional silanes such as methyltrichlorosilane, trimethoxysilane, chloromethyltrimethoxysilane, phenyltrimethoxysilane and trifluoropropyltrimethoxysilane; and tetrafunctional silanes such as tetrachlorosilane, tetramethoxysilane and tetraethoxysilane.
Aside from the above-mentioned monomers, prepolymers obtained from such monomers are also useful as the starting reactant.
In the synthesis of the organopolysiloxane, various reaction catalysts and solvents may be used if necessary. Using such a catalyst and solvent, reaction may be carried out in a conventional well-known manner.
If silanol groups are left in the organopolysiloxane (A), the platinum group metal catalyst (C) may promote dehydrogenation reaction between the silanol groups and the organohydrogenpolysiloxane (B) to induce foaming. It is then recommended to previously cap the silanol groups in the organopolysiloxane (A) with a silylating agent such as hexamethyldisilazane.
The organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond should preferably be liquid. Specifically, the organopolysiloxane should preferably have a viscosity of 500 to 50,000 centipoise (cP) at 25xc2x0 C., and especially 1,000 to 20,000 cP at 25xc2x0 C. If the organopolysiloxane is solid, it is dissolved in a solvent prior to use.
Component (B) is an organohydrogenpolysiloxane containing a cyanoalkyl group, which is preferably represented by the average compositional formula (II).
R4kR5mR6nSiO(4+k+m+n)/2xe2x80x83xe2x80x83(II)
Herein R4 is a cyanoalkyl group having 3 to 5 carbon atoms, R5 is hydrogen, R6 is a monovalent hydrocarbon group having 1 to 10 carbon atoms other than R4, letter xe2x80x9ckxe2x80x9d is a number of 0.2 to 0.7, xe2x80x9cmxe2x80x9d is a number of 0.2 to 0.7, xe2x80x9cnxe2x80x9d is a number of 1.0 to 1.6, and k+m+n is 2.0 to 2.3.
Examples of the C3-C5 cyanoalkyl group represented by R4 include cyanoethyl, cyanopropyl, cyanobutyl, 2-cyanopropyl, 2-cyanobutyl, 3-cyanobutyl, and 2-methyl-2-cyanopropyl, as exemplified for R1. Of these, cyanoethyl is preferred.
R6 is selected from substituted or unsubstituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, other than R4, preferably free of aliphatic unsaturation, for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl and cyclohexyl, aryl groups such as phenyl, aralkyl groups such as benzyl and phenylethyl, and halogenated monovalent hydrocarbon groups such as chloromethyl, bromoethyl, 3,3,3-trifluoropropyl, 1,1,1-trifluorohexyl and 3-chloropropyl. Of these, methyl, ethyl, propyl and phenyl are preferred, with methyl being most preferred.
The letter xe2x80x9ckxe2x80x9d representative of the content of cyanoalkyl groups in the average compositional formula (II) is from 0.2 to 0.7, and preferably from 0.3 to 0.6. Too low a cyanoalkyl content leads to a lower concentration of nitrile groups in the polymer, which may lead to a reduced dielectric constant. Another potential problem is that the organohydrogenpolysiloxane with a lower cyanoalkyl content becomes less compatible with the organopolysiloxane containing a cyanoalkyl group and a monovalent hydrocarbon group having an aliphatic unsaturated bond (A), leading to insufficient cure or failing to produce uniformly cured parts. With too high a cyanoalkyl content, the content of hydrogen atoms (represented by xe2x80x9cmxe2x80x9d) may be relatively reduced, resulting in insufficient cure.
The letter xe2x80x9cmxe2x80x9d representative of the content of hydrogen atoms (i.e., SiH groups) is from 0.2 to 0.7, preferably from 0.3 to 0.6. A hydrogen content below the range may lead to insufficient cure. With too high a hydrogen content, the content of cyanoalkyl groups (represented by xe2x80x9ckxe2x80x9d) may be relatively reduced to thereby lower the concentration of nitrile groups in the polymer, which may lead to a reduced dielectric constant. In addition, the composition may encounter a foaming phenomenon by hydrogen gas.
The letter xe2x80x9cnxe2x80x9d representative of the content of substituted or unsubstituted monovalent hydrocarbon groups is from 1.0 to 1.6, preferably from 1.0 to 1.2. A too large value of n may lead to a reduced content of cyanoalkyl groups or hydrogen atoms (SiH groups).
The sum of k+m+n in the average compositional formula (II) is from 2.0 to 2.3, preferably from 2.0 to 2.1. If k+m+n is below the range, the organohydrogenpolysiloxane may become age unstable and the cured product become very brittle and impractical. If k+m+n is above the range, the composition may under-cure, precluding film formation.
In preparing the organohydrogenpolysiloxane having a cyanoalkyl group, represented by the average compositional formula (II), any conventional organohydrogenpolysiloxane synthesis methods may be used, with no need to limit to a special method. Illustratively, the end product can be obtained by effecting equilibration reaction between a cyanoalkyl group-containing organopolysiloxane and an organohydrogenpolysiloxane in the presence of a strong acid such as sulfuric acid or trifluoromethanesulfonic acid. By adding a terminal group-providing compound such as hexamethyldisiloxane during the equilibration reaction, the type of terminal functional group and the degree of polymerization can be adjusted in accordance with the type and amount of the compound.
The silanes, which are used as raw materials for the organohydrogenpolysiloxane containing a cyanoalkyl group, should preferably further have at least one hydrolyzable functional group directly attached to a silicon atom. Such hydrolyzable functional groups include halogens, OR, OCOR and NRRxe2x80x2 wherein R and Rxe2x80x2 are hydrogen or alkyl as defined above.
The silanes used as the raw materials include silanes having a cyanoalkyl group, examples of which include monofunctional silanes such as cyanoethyldimethylchlorosilane, cyanopropyldiethylmethoxysilane, cyanoethyldimethylacetoxysilane and dicyanoethylmethylmethoxysilane; difunctional silanes such as cyanoethylchloromethyldichlorosilane, cyanoethylmethyldimethoxysilane, cyanoethyltrifluoropropyldiethoxysilane and cyanopropylphenyldiaminosilane; and trifunctional silanes such as cyanoethyltriethoxysilane and cyanobutyltrimethoxysilane. Of these, the difunctional silanes are preferred. In the equilibration reaction, prepolymers obtained from the above-mentioned monomers are preferably used.
Examples of the silane having a SiH group used as the raw material for the organohydrogenpolysiloxane include methylhydrogensilicone fluid and tetramethyltetrasiloxane.
Exemplary of the terminal group-providing compound are hexamethyldisiloxane and tetramethyldisiloxane. If necessary, cyclic organopolysiloxanes such as octamethyltetrasiloxane may be used.
The hydrogenpolysiloxane having a cyanoalkyl group should preferably have a viscosity of 300 to 50,000 cP at 25xc2x0 C., more preferably 500 to 10,000 cP at 25xc2x0 C.
Components (A) and (B) are blended in such amounts that 0.5 to 4, especially 0.7 to 1.2 hydrogen atoms directly attached to silicon atoms (i.e., SiH groups) in component (B) are available per aliphatic unsaturated bond, typically alkenyl group, in component (A). Less SiH groups may lead to insufficient cure whereas excessive SiH groups may allow hydrogen gas to provoke a foaming phenomenon.
The platinum group metal catalyst (C) may be any of well-known catalysts customarily used in hydrosilylation. Often, platinum and platinum compounds are used. Typical examples include chloroplatinic acid, alcohol solutions of chloroplatinic acid, the reaction products of chloroplatinic acid with alcohols, the reaction products of chloroplatinic acid with olefins, and the reaction products of chloroplatinic acid with vinyl-containing siloxanes.
The platinum group metal catalyst is used in a catalytic amount which may be adjusted in accordance with a desired cure rate. From the economic standpoint or to provide effective cure, the catalyst is preferably used in such amounts as to provide 1 to 10,000 parts, especially 10 to 7,000 parts by weight of platinum group metal per million parts by weight of components (A) and (B) combined.
In the composition of the invention, reaction regulating agents, reinforcing agents, additives (e.g., pigments, parting agents, heat resistance modifiers, flow modifiers, anti-settling agents, adhesion modifiers, heat conductive fillers, and electrically conductive fillers), diluents and the like may be optionally blended as long as they do not compromise the objects of the invention.
The composition of the invention may be prepared by intimately mixing components (A) to (C) and optional components at room temperature. Mixing may be done in a conventional way.
The composition thus obtained is preferably liquid. It should preferably have a viscosity of 300 to 50,000 centipoise (cP) at 25xc2x0 C., especially 500 to 20,000 cP at 25xc2x0 C.
For curing, the composition may be heated at a temperature of 100xc2x0 C. or higher, more preferably 100 to 150xc2x0 C., for about 1 to 120 minutes. In general, the more the amount of component (C) used, the faster cures the composition.
The highly dielectric addition curable composition of the invention has many advantages. It is easy to handle because of a liquid state even in the absence of a solvent and a relatively low viscosity and effectively curable. It has an ability to form a tough clear film. The cured composition has a large dielectric constant, a low dielectric loss, and a low volume resistivity, as well as a low moisture absorption as compared with other cyanoethyl polymers, a high heat decomposition temperature and heat resistance. Because of these improvements, the composition is advantageously applicable in the electronic material field.
The compositions of the invention are suited for use in electric and electronic parts requiring a high dielectric constant, for example, as the binder in electroluminescent devices, the film material in capacitors, and other dielectric materials. The compositions, combined with various electrically conductive fillers, find use as antistatic materials, electrostatic dissipating materials and electric conductive materials requiring a low volume resistivity. Additionally, the compositions can be utilized in general applications to form films, sheets, coatings and foams.